An alcohol thermometer is a commonplace item for many households. Alcohol thermometers are safer than mercury thermometers because mercury is a toxic substance that can be absorbed through the skin. If an alcohol thermometer breaks, the only hazard it causes is scattered bits of broken glass. However, alcohol-based thermometers have limitations.
Low Boiling Point
Alcohol has a low boiling point. Therefore, it cannot be used in places with high temperatures. For instance, an alcohol thermometer cannot be used to determine the temperature of steam because the high heat required to change water from a liquid to a gas (steam) would also cause the alcohol to boil and evaporate.
Alcohol has a low surface tension and does not react quickly to temperature changes, nor is it a good conductor of heat. This physical property also makes alcohol prone to vaporisation, making it less reliable to use than mercury in a thermometer. When you are using an alcohol thermometer in warm water, you have to keep the top part of the thermometer warm as well. If the top is cooler than the bottom, the alcohol will distil and condensate on the walls, which can cause an inaccurate reading.
Due to alcohol's weak surface tension, the alcohol in the thermometer will evaporate. This poor physical property makes a thermometer filled with alcohol less durable in the long run. The typical shelf life of an alcohol thermometer is significantly shorter than that of a mercury thermometer. This loss of fluid cannot be avoided.
- University of Wyoming: A thermometer comparison
- Heat for advanced students By Edwin Edser. Macmillan and co, limited, 1920
- Explaining Physics: GCSE Edition By Stephen Pople. Oxford University Press, 1987
- Sea Friends: Measuring temperature how temperatures are measured
- BIPM: Liquid in Glass Thermometry